Conventional rotary windmills have been used for hundreds of years to generate mechanical work from wind energy and more recently to generate electric power from wind energy. Rotary windmills have a number of disadvantages. The blades are generally, large, expensive and require a tower or mast of substantial height for blade ground clearance. Such units must be very large to be efficient and economically viable, and require professional supervision and considerable maintenance. They will not generate at wind speeds below about 20 mph, and must be feathered to avoid destruction at wind speeds above about 45 mph. The rotary converters which transform wind energy to electric power are relatively expensive, low efficiency and subject to wear. Only a relatively small cross-section area of the wind on the blades is actually useful for driving the blades.